In sheet-fed rotary presses, a sheet turnover mechanism is disposed in the sheet transport path in order to turn the sheet over. Normally, the sheet is transported with its front edge leading through the entire machine and only the top of the sheet is printed. If the sheet is to be printed on both sides, the sheet turnover mechanism is switched over between two printing units, as a result of which the trailing edge of the sheet becomes the leading edge. Thus to turn the sheet over, the relative position of the adjacent printing units must be changed so that the trailing edge can now be transferred here instead of the leading edge of the sheet. To change the relative position of the sheet edges, the transmission line in a press of this kind must be capable of being disconnected. Double gearwheels have been known for this purpose for many years. In a double gearwheel of this kind, a gearwheel ring is fitted on a main gearwheel and is frictionally connected to the main gearwheel by a clamping mechanism. Such mechanisms hitherto consisted of clamping shoes or a clamp ring and the clamping elements were individually tensioned manually. In the course of the further development of printing presses, the procedure adopted was to render the clamping mechanisms such that they can be automated in order to avoid tedious manual operation.
A mechanism of the foregoing kind is generally described in DE-PS 35 34 488. In this mechanism for clamping together two gearwheels in a sheet-fed rotary press which can be set from single-sided printing to perfecting printing, the clamping force is applied by a spring which, for the purpose of cancelling the clamping effect, can be loaded by a pneumatic piston or bellows. Clamping is by means of one-armed crank levers which are connected by bolts to the clamping shoes in order to clamp the gearwheel ring. The one-armed crank levers are mounted on ball elements and, on movement, produce in the point of articulation of the bolt an axial displacement with respect to the clamping shoes.
As a result of the above, a clamping force is applied to the clamping shoes with the pivoting movement of the levers. The pivoting movement of the levers is produced by a guide element in which the ends of the levers engage and the guide element is mounted on a rod centrally with respect to the main gearwheel. The rod is connected to the gearwheel drive journal so as to be axially displaceable and is loaded outwardly by a compression spring. The outer end of the guide rod is guided in a rolling bearing and the bearing is mounted in a receiving element which is, in turn, connected to a pneumatic bellows.
Normally, the compression spring presses the guide element outwardly and thus, by way of the levers, locks the clamping between the gearwheel ring and the main gearwheel. On the changeover, the bellows is subjected to compressed air and displaces the guide element against the gearwheel under the load of the compression spring and in so doing releases the clamping between the gearwheel ring and the main gearwheel.
The mechanism just described has a number of disadvantages. In particular, the elements for generating the clamping are relatively complex and are mounted so as to be fixed to the cylinder. Thus they also rotate during complete operation. In addition, the force transmission is very complex. Another problem is that the bellows bears between the housing wall and the cylinder against the force of the compression spring. Consequently, on the release of the clamping an axial force is applied to the cylinder bearings and may result in a shift of the entire cylinder and hence also of the gearwheels.
The above problem is obviated in a mechanism according to DE-PS 31 27 539. As disclosed in this reference, the mechanism for clamping and releasing two gearwheels again comprises a main gearwheel with a rotatable gearwheel ring fitted thereon. Clamping is produced by way of individual bolts loaded by compression springs. The tensioning force for the compression springs is produced by a combination of two elements by means of rotary wedge surfaces. Basically, these rotary wedge surfaces each correspond to a screwthread turn. Rotation of the two elements in relation to one another thus results in a change in spacing.
One of the two elements has its rotary wedge surface facing the gearwheel and is non-rotatably connected to a tensioning plate for the gearwheel ring. The second element, which is directed with its rotary wedge surface towards the first, is disposed between the first element and the tensioning plate. The second element is also provided with a toothing on its outside. A gearwheel mounted rotatably on the cylinder journal engages this toothing.
By rotating the middle element with its rotary wedge surface it is now possible to vary the distance of the outer element with its rotary edge surface from the tensioning plate. The deflection of the compression spring on the other side of the main gearwheel is altered in these conditions and hence so is the tensioning force between the tensioning plate and the gearwheel.
To eliminate the clamping, therefore, the inner rotary wedge element is turned until the distance between the outer rotary wedge element and the tensioning plate is minimal. As a result the tensioning force of the compression spring is also minimal and the gearwheel ring can be moved on the main gearwheel. For clamping purposes the inner rotary wedge element is again moved to the highest point to produce the highest clamping force.
The arrangement of this reference obviates transmitting external forces into the arrangement comprising the gearwheel, gearwheel ring and clamp elements and the cylinder bearings. However, all the elements required for clamping and releasing the clamping again have to be mounted on the gearwheel and consequently also rotate during the entire operation. In addition there is the difficulty that a gearwheel required only for release purposes has to be mounted on the cylinder journal and accordingly also rotates continuously. The entire operation and, in particular, assembly, are rendered difficult as a result. The final and most important argument is that the drive forces required to turn this mechanism are very high since the friction between the rotary wedge surfaces is very considerable.
From DE 3,611,324 C2 there is known a further device for releasing a frictional connection of a double gearwheel consisting of main gearwheel and a concentric toothed gear ring. A tensioning disc is formed, essentially in its middle part, as an operating piston, which is disposed with a corresponding part of the main gearwheel as a hydraulic system. By energizing the hydraulic system, the tensioning force is overcome and the gear ring is released.
A disadvantage of this system is that the complete device is arranged on the cylinder dowel pin and, therefore, revolves during machine operation. Accordingly, considerable masses must be moved and also there is the danger of leakage in the hydraulic system.
In other known mechanisms, all the elements required for locking and releasing the clamping, and the drive elements provided for the purpose, are mounted on the gearwheel. The entire unit of this double gearwheel can admittedly be made relatively compact but becomes very complex and heavy. There is largely no thought of externally controlled actuation.
The problem is therefore to provide a clutch mechanism for releasing a frictional connection in a double gearwheel drive of a sheet-fed rotary press adapted to be converted from regular one-sided printing to two-sided perfecting printing wherein the clamping effect can be released without axial loading of the cylinder and its bearings and with minimum modification of the drive gearwheel. In addition, the mechanism for releasing the clamping should not have to co-rotate during operation of the press, thus greatly reducing the weight of the drive gearwheel.